Post-combustion coal CO2 capture and conversion is an urgent problem because in the next decade China will be adding 800,000 MW of coal power — 250% of the present coal-fired power plants in the US. Coal combustion is the largest source of CO2.

Co-sited concentrating solar and natural gas are now being discussed http://www.powermag.com/ issues/ features/ Fossil-Fuels-+-Solar-Energy-The-Future-of-Electricity-Generation_1797.html and the marriage of coal and wind might be next.

This green gird is covering an area about 10 times larger than Denmark, so the variability should be much less.

Usually it applies to home PV setups — instead of buying a massive block of batteries to store excess power in the day and use it overnight yourself, you just “store” it on the gird — sell your surplus during the day, then buy it “back” at night. This works nicely given that overall demand is usually much higher during the day.

For wind power, perhaps the term “buffering” would be better than “storage”, as the effect needed is to have many geographically-dispersed turbines available to the same pool of consumers. If set up correctly, odds are nearly certain that there will be enough wind blowing somewhere among the turbines to provide for the power needs at any given moment.

Of course, then, some actual storage might still be desired, to bring the reliability from 98% or 99% up to fully 100%, while dropping the traditional CO2-producing “baseload” sources down to zero. Fortunately, the transition should be gradual (e.g. natural gas will remain acceptable for a while to replace coal, and it’s production can be fully controlled and easily adjusted), so there will be enough time for the population of car batteries to grow to fill this need — provided these new “green” grids are truly smart grids that can communicate price signals to/from the cars.